Put all points into a shapefile, either by manually entering them in QGIS, or by putting them into a csv and loading it into QGIS.
Buffer the points which are the center of any arc by the given distance (yes, you'll have to convert to km first), then manually draw the polygons using snapping by connecting the points and arcs in the correct order.
Also, note on the side: The common combination of QGIS and shapefile can't do curves. Anything which poses as a curve or circle is just enough points connected by short, straight lines so they seem to form a curve. As @ndawson pointed out, there are some file types which are able to store true curves, and you also are able to manually add curves via the shape digitzing toolbar (https://docs.qgis.org/testing/en/docs/user_manual/working_with_vector/editing_geometry_attributes.html#add-circular-string).